1. Field of the Invention
The present invention relates to a probe test apparatus for measuring electric properties of an object such as the semiconductor device to be checked.
2. Description of the Related Art
In the conventional probe test apparatus, a wafer cassette is mounted on a cassette-mounted stage in such a way that its wafer take-in and -out opening faces the rear side of the apparatus, when the operator sets it on the stage by his hands. When it is not positioned at its correct area on the cassette-mounted stage, the correct holding of a wafer W may not be attained or the wafer W may be damaged upon taking the wafer W into and out of it. This is the reason why it must be positioned at its correct area on the cassette-mounted stage. However, the cassette-mounted stage is enclosed by side plates of the apparatus itself and the operator cannot therefore see and confirm the stage by his eyes. This makes it difficult for the operator to position it at its correct area on the stage.
Further, wafers having 6 and 8-inch diameters are commonly checked by one probe test apparatus in the conventional cases. It is therefore needed to previously confirm which of them is to be checked. The conventional wafer size detector section is arranged not on the passage through which the wafer W is carried from the cassette to a wafer-mounted stage, but at a different place. When the size of a wafer W is to be detected, therefore, a pincette of the load/unload unit must be swung to position the wafer W at the wafer size detector section. This means that the load/unload unit needs another drive shaft for swinging the pincette, in addition to a drive shaft for linearly forwarding and retreating it to take the wafer W into and out of the cassette. The load/unload unit, therefore, becomes complicated, comprising a combination of two drive shafts. In addition, the cycle time during which the wafer W is taken into and out of the cassette is long in the conventional probe test apparatus.